Genetically modified cotton has no effect on arbuscular mycorrhizal colonisation of roots

There is conjecture that genetically modified (GM) plants, expressing insecticidal or herbicide tolerance traits, do not form mycorrhizal symbioses. For cotton, Gossypium hirsutum, which is grown worldwide as a high and low input crop, such an issue would be of concern because it depends upon symbiosis with arbuscular mycorrhizal (AM) fungi for uptake of immobile elements, such as phosphorus and zinc, and GM cotton varieties are widely grown. We compared mycorrhizal development in commercial cultivars of cotton expressing genes for insect resistance (Cry1Ac and Cry2Ab), glyphosate tolerance (5-enolpyruvylshikimate-3-phosphate synthase gene (EPSPS)), or both, and their conventional parent line. AM development in cotton roots increased rapidly in the first three weeks after sowing, reaching a plateau level of around 70–80% root length. The observed pattern of colonisation was virtually identical among both conventional and GM cultivars of cotton at each assessment, clearly indicating that colonisation by AM fungi were not affected by the expressed transgenic traits.